494
FXUS63 KTOP 291929
AFDTOP

Area Forecast Discussion
National Weather Service Topeka KS
229 PM CDT Fri Aug 29 2025

.KEY MESSAGES...

- There are good chances (50-80%) for showers and storms
  beginning Saturday night and lasting through Monday.

- Average rain totals could end up being around an inch or a
  little more by Monday evening.

- A cold front with Canadian air is forecast to push south
  Wednesday, bringing cool temperatures to end next week.

&&

.DISCUSSION...
Issued at 229 PM CDT Fri Aug 29 2025

19Z water vapor imagery showed a low amplitude ridge centered
over NM while a closed low spun off the OR coast and shortwave
activity progressed across the northern plains and Canada.
Surface obs showed surface high pressure has been gradually
weakening with low pressure in the lee of the central Rockies.
The weak surface pattern has kept the boundary layer RH from
mixing out much.

The forecast for Saturday through Monday is expected to be
driven mainly by shortwave energy that rounds the top of the
ridge and gradually strengthens into a slow moving low pressure
system. Some solutions even close the system at the surface.
This should provide a prolonged period of forcing for vertical
motion and precip chances beginning Saturday afternoon and
continuing through the day Monday. The better dynamics are
progged to impact the forecast area Saturday night and Sunday as
the system becomes closed. There is decent moisture available
with PWs around 1.5 inches, so there could be periods of
moderate rainfall. Instability appears to be limited though as
models prog mid level lapse rates to be rather weak around 5.5
C/km. So the expectation is for showers with embedded thunder to
be possible. Kept POPs generally in the 50 to 70 percent range
as coverage at any given time could end up being more scattered.
The increase cloud cover and precip chances are forecast to
keep afternoon highs in the lower and middle 70s for Sunday and
Monday.

The low pressure system is progged to open up and propagate to the
southeast of the forecast area by Tuesday bringing dry weather. The
next big weather feature is expected to be a cold front that moves
through Wednesday with another Canadian high pressure system
building south. The NBM is giving a slight chance POP for
precip with the frontal passage which looks like a result of
some differences with the upper trough and shortwave energy that
propagates through it. The 00Z ensemble cluster analysis showed
about a third of the ensemble members had the upper trough
further east with the better forcing into the Upper Midwest and
Great Lakes. This seems to fit with the operational GFS
solutions. Meanwhile the ECMWF is further west with the upper
trough and brings the center of the surface high through the
plains rather than a glancing blow like the GFS. Given the lower
confidence in the operational models and spread among the
ensembles, have stuck with the NBM which weights the ECMWF a
little more heavily. The NBM temps seems to fit within the 25th
to 75th percentile of the ensemble range so it should be a good
first forecast. This forecast calls for lows in the upper 40s
for Thursday morning while highs only make it to around 70.
Given the significant proportion of the ensembles supporting the
GFS solution, I would expect some adjustment to the temp
forecast over the coming days as models hopefully converge on a
common solution.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1151 AM CDT Fri Aug 29 2025

Southerly low level flow is expected to keep the boundary layer
RH relatively high, setting up the potential for more stratus
and fog tonight. Increasing high clouds and warmer low temps has
me leaning more towards stratus with maybe some MVFR fog. As
for precip chances, models tend to keep QPF to the west of MHK
through 18Z Sat. Probabilities for SHRA look to increase after
18Z as a slow moving disturbance approaches.

&&

.TOP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Wolters
AVIATION...Wolters